Mechanical systems such as engines and transmissions utilize a lubricating oil or other fluid to dissipate heat within the system and to reduce wear on system components. However, due to the nature of the systems, wear does occur, resulting in the presence of small metallic particles in the oil or other lubricating fluid.
Due to the normal wear and the natural breakdown of the oil or other lubricating fluid, the lubricating fluid in such systems must be changed periodically. This is typically done on a time or usage basis, for example, every 90 days or 2000 hours of use. While small metal particles may result from normal wear, larger particles are usually an indication of abnormal wear or a more serious problem. For example, the resulting wear creates abnormal amounts of metal particles within the lubricant. Under normal maintenance procedures, the metal particles would be present in the lubricant for an extended period of time. If this condition is not identified and the appropriate repairs completed, more expensive repairs including the replacement of major system components may result.
Detection of metallic particles in hydraulic systems is equally important as hydraulic systems represent large expenses in the event of component failure. If failures are detected early, repair expenses can be minimized; however, if catastrophic failure occurs, the large amounts of particles caused by the failure can enter the hydraulic system and cause damage to many other components. Fortunately, any catastrophic failure of one of the components is often preceded by the gradual breakup of one or more components. If this breakup can be detected, corrective action can be taken before any further damage to surrounding components occurs.
In the past, there have been several different ways to detect metallic particles within a fluid. One such system is described in U.S. Pat. No. 4,219,805. This system captures ferrous particles that are contained in a fluid medium, and indicates the mass of any significant individual ferrous particles and the total mass of such particles that have accumulated over a predetermined time period. However, this system is limited to the detection of ferrous particles, e.g., iron, as opposed to non-ferrous particles, e.g., copper, brass, or non-magnetic stainless steel.
In U.S. Pat. No. 5,502,378 assigned to the assignee of the present application, a sensor is disclosed that detects particles within a fluid that is generally comprised of a housing defining a cavity and a magnet disposed adjacent to the cavity bottom to attract particles into the cavity. A first coil is wound about the surface of the cavity. The induction of the first coil is responsive to the particle accumulation within the cavity. A second coil is wound about the magnet. The induction of the second coil is responsive to the temperature of the fluid and is independent of the particle accumulation within the cavity. This sensor is unable to distinguish between ferrous and non-ferrous particles.
Still further, in U.S. Pat. No. 5,608,315 assigned to the assignee of the present application, a sensor is disclosed that detects both ferrous and non-ferrous particles, this particular sensor utilizing four separate coils. In this sensor configuration, a first coil is provided for responsiveness to both ferrous and non-ferrous particles, a second coil is provided for responsiveness to the accumulation of ferrous particles only, and yet a third coil is provided as a reference coil for temperature measurement. A fourth electromagnetic coil is provided to attract particles into the proximity of the second coil measuring the ferrous particles. All four coils are wrapped around a bobbin. This sensor construction is very complex because the bobbin is a special part that limits the application of the sensor to different machines and the use of four separate coils requires additional electronics for the sensing of the metallic particles.
It would therefore be desirable if there were provided a fluid particle sensor that would more reliably detect both ferrous and non-ferrous materials in a fluid medium; that would provide easier maintenance and installation; and that would be much simpler in overall design.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.